So I've narrowed it down to Tough or Great Weapon Master. One question about GWM though, how does that interact with Reckless Attack? Does the -5 to attack apply to both rolls from Reckless Attack? 

Lets say a creature has an AC of 16. I use reckless attack and GWM. I roll (with mods added) a 17 and a 14. Would I be able to hit still with the 17, or does the -5 from GWM bring both rolls down to a 12 and 9 respectively, therefore a miss?

Is GWM better than Tough? I'm honestly leaning towards Tough but idk. Are there any other feats I should be considering? Lucky seems pretty OP as well.

I could also use the ability modifier to bring both my CON and DEX mods up by 1 point (17 CON and 13 DEX currently, so improving those by one each would give me the next higher modifier on both).  

Essentially its between Tough, GWM, or improving CON and DEX mods by 1 each and gaining 2 to my AC (would make my AC 16).

Any advice or recommendations? Thanks so much in advance!

Quote from Aerick69 >>

Lets say a creature has an AC of 16. I use reckless attack and GWM. I roll (with mods added) a 17 and a 14. Would I be able to hit still with the 17, or does the -5 from GWM bring both rolls down to a 12 and 9 respectively, therefore a miss?

 You roll with advantage and apply the penalty after rolling, so this is correct -- as soon as you've seen which number on the d20 is higher, that is the result of your roll and what you apply all modifiers and penalties to, you ignore the other die entirely.

What is your STR? If it's not at 20, getting that up would also be good, but getting CON and DEX up isn't bad. Also, do you know what level your campaign is going to? Knowing whether you have room for ASI and feats can be useful in setting priorities.

Lol my strength is a 20. I rolled unbelievably well while creating my barb and my half-orc traits gave me a plus 2 to strength, so yeah I got lucky with that ability.  

I dont know how far we're going, but I know my DM isn't putting a cap on our levels or anything. He's pretty lenient with stuff( i.e. letting me keep my 20 strength at level 1 lol). 

After reading a little more I think Im going to take GWM and maybe do the ability mods at level 8. My mods have been pretty sufficient so far and I haven't really needed an AC boost or even DEX/CON boosts. Danger Sense gives me advantage on DEX saves and I have proficiency in CON saves. My shield gives me a +1 to AC anyways, so my base is a 14 but a 15 with the shield. As we face higher level enemies, I have a feeling theyll be able to hit a 17 if I went that route.

He means, what level will you guys play and end at? 8? 10? 12? It affects your build. I never plan my characters to hit 20, because I have yet to be in a campaign that was 1-20. 

With Advantage, all it is, is that you roll two d20s, and you get to pick the highest as your d20 roll. So if I roll 2d20 abd get a 6 and a 14, then it acts as though I rolled a 14 (and Disadvantage works the reverse - it would act as though I'd rolled a 6). So you'd take the highest of the two rolls, then apply your bonuses.

After reading a little more I think Im going to take GWM and maybe do the ability mods at level 8. My mods have been pretty sufficient so far and I haven't really needed an AC boost or even DEX/CON boosts. Danger Sense gives me advantage on DEX saves and I have proficiency in CON saves. My shield gives me a +1 to AC anyways, so my base is a 14 but a 15 with the shield. As we face higher level enemies, I have a feeling theyll be able to hit a 17 if I went that route.

What is your preferred weapon of choice or fighting style? If you use heavy weapons then the GWM if a solid option to consider. But if you are not sure about committing to this fighting style then you might want to consider another option at this stage.  Heavy weapons require two hands, so you won't have a free hand, or carry a torch, or wield a shield. This is not to deter you from choosing GWM; but consider you are committing to a set of weapons in order to get the full benefit of the feat. With that said, if you like swinging a maul then GWM is an option worth taking. 

Regarding the Ability Score Improvement, it won't just improve your AC and saving throws.  The CON gives you another hit point per level and the DEX increase helps with your range weapons attacks and Stealth (attributes that come up often over campaign play).  And getting a default AC of 16 is pretty good spot to be in. 

Since you have the 20 str already I would 100% go gwm.  I would then go to 5 to get your 2nd attack, and after that depending on what level the campaign is going to end at, swap over to fighter the rest of the way.  At lvl 9 fighter 4 get pole arm master, at lvl 11 fighter 6 bump an asi or get sentenal.  Lvl 13 fighter 8 asi or mobile.  

If you're not already locked into your race you can take custom lineage, be an orc for flavor and have the free feat at lvl 1.  

That way right at lvl 5 your build is mostly online.  

Free feat as a marshal class at lvl 1 is a massive power spike.  

Tough is honestly a bit of a trap as far as feats go.  It looks good on paper but overall it really doesn't add much in actual gameplay- generally you'll only gain an average of one extra hit out of it.  GWM is a great feat for a barbarian- getting an extra attack as a bonus action every time you drop a foe or crit is useful all by itself and the damage boost stacks extremely well with Reckless Attack.